Nickel-manganese-ferrous ferrite



Feb. 22, 1963 H BIN IM. ETAL 3,236,777

Nl' CKEL-MANGANESE-FERROUS FERRI TE Fil ed April 121 1963 MANGANESE FERRITE Mn H3 0 I00 AM A W m /MN A E L I I00 so 70 60 5o 40 3o 20 19 loo Ni F9204 Fe F9204 NICKEL FERRITE FERROUS FERRITE COMPOSITION DIAGRAM (MOLE INVENTORS HO BIN IM DONALD G. WICKHAM ATTORN EY United States Patent 3,236,777 NlCKEL-MANGANESE-FERRDUS FERIRITE Ho Bin Im, Los Angeles, and Donald G. Wickham, Santa Monica, Calif., assignors to Ampex Corporation, Culver City, Calif, a corporation of California Filed Apr. 12, 1963, Ser. No. 272,753 Claims. (Cl. 252-625) This invention relates to a new composition of matter. More particularly, this invention pertains to a new family of ceramic ferromagnetic materials commonly termed broadly as ferrites.

Magnetic ferrite material has found extensive use in recent years. The particular application of such material with which this invention is concerned lies in the memory and switching applications in digital computers, and various data processing equipment. This application involves the use of microsecond pulses for the handling of information expressed in a binary code.

Rectangular hysteresis loop properties .are required to provide two stable states of remanent magnetization and to provide a highly non-linear B-H relationship so that the state of magnetization can be definitely and quickly changed. The degrees of rectangularity and the uniformity and stability of characteristics have a direct bearing upon the number of cores which can be used reliably in a memory and, upon the storage capacity of the memory. The values of coercive force determine how rapidly the information can be handled. The ferrite used in this application is usually of the manganese-magnesium variety. This invention, as will be shown, involves a new and greatly improved variety of ferrite for the above purpose.

As previously indicated, the predominant number of memory cores presently utilized are substituted magnesium-manganese ferrites similar to those described in United States Patent No. 2,981,689. This particular family of ferrites exhibit low coercivities and fast switching speeds relative to most other ferrite materials. However, the most serious disadvantage relative to the utilization of magnesium-manganese ferrites is that their coercivity decreases very rapidly with increasing temperature. This disadvantage is most pronounced when the cores are to be operated in devices that necessarily undergo temperature changes. The presently available ferrites which have small temperature coefiicients of coercivity alternatively possess high values for the coercivity. As a result, these cores require undesirably large driving currents. An example of these latter materials are the magnetically annealed nickel-ferrous ferrites as described in United States Patent No. 3,055,832.

An object of this invention is to provide a new ferrite composition having improved properties for use as memory core elements of computers.

An additional object of this invention is to provide a new family of ferrite materials which exhibit improved.

properties over a wide range of temperatures when used as the bistable magnetic memory elements of computers. A further object of this invention is to provide a new family of ferrite materials which require no current compensation over a temperature range exceeding 100 C.

3,236,777 Patented Feb. 22, 1966 A still further object of this invention is to provide a new family of ferrite materials Which exhibit the combination of low coercivity, low temperature coefiicients of coercivity and fast switching speeds previously unobtained.

These and other objects will become more apparent from the following detailed description in which the figure is a composition ternary diagram depicting the compositions of this invention.

The novel ferrite compositions of this invention are comprised of nickel ferrite, NiFe O manganese ferrite, MnFe O and ferrous ferrite FE Fe O Reference is had to the mole percents of each constituent contemplated shown and disclosed as bound by the area ABCD on the ternary diagram of the figure. It has been discovered that the particularly desirable properties aboveenurnerated are possessed by compositions lying within the area ABCD. The compositions as found at each point as shown in the figure are as follows:

(A) 75 mole percent NiFe O 20 mole percent MnFe O 5 mole percent Fe O (B) 30 mole percent NiFe O 65 mole percent MnFe O 5 mole percent Fe o (C) 40 mole percent NiFe O 35 mole percent MnFe O 25 mole percent Fe O (D) 65 mole percent NiFe O 10 mole percent MnFe O 25 mole percent Fe O As will be subsequently shown, the compositions lying within the above rectangle possess the highly desirable properties discussed. However, such properties were not found in binary systems represented by the sides of the diagram.

Particularly outstanding compositions embraced within the area ABCD of the figure are ones including 60 mole percent nickel ferrite, 20 mole percent manganese ferrite and 20 mole percent ferrous ferrite; 55 mole percent nickel ferrite, 25 mole percent manganese ferrite and 20 mole percent ferrous ferrite; 40 mole percent nickel ferrite, mole percent manganese ferrite and 15 mole percent ferrous ferrite; 40 mole percent nickel ferrite, mole percent manganese ferrite, and 10 mole percent ferrous ferrite. The superior performance of these prefered compositions will become readily apparent from the results as shown in Table 11 below.

Generally, minor amounts of impurities may be present in the compositions of the invention as contemplated. It is preferred that such impurities do not exceed 2 mole percent of the composition. Illustrative, but not limiting examples of such impurities include, zinc, tin, lithium, and aluminum. The only element found to be definitely detrimental when present in amounts exceeding traces is cobalt.

To indicate the pulse-response behavior of a typical core prepared according to this invention compared with a typical fast-switching magnesium-manganese ferrite core of the same size (which is on the order of 0.05 in. 0.1)., 0.03 in. I.D., 0.017 in. height) reference is had to Table I below:

TABLE I Core Full Driving Current.

Disturbing Current Pulse Rise Switchturbed Output Voltage Zero dV1 Voltage (mv.) z

Temp. Limits t Time Time t. s (,u eC.) seo) This Invention 1 Mg-Mn-Ferrite oi the art- 1 0.4 (NiFezOr) 0.5 (MnFego 0.1 (F6304).

As can be seen from Table I, the composition of this invention provided greatly improved properties in the areas of prime importance to its use as a core in a computer device. Of particular note is the improved switching time and the higher temperature limit. The importance of these will be further explained in the following discussion and tables.

The manufacture of the material of this invention and the fabrication of ceramic toroids is carried out in a manner similar to that ordinarily employed for other ceramic ferrites. Briefly, the procedure consists of mixing the raw materials, reacting them, grinding the product, adding binders and lubricants, pressing into toroids, and sintering at a high temperature in the absence of air at temperatures between 2350 F. and 2500 F. Samples are cooled from the sintering temperature to a lower temperature such as 1900 F., and then cooled quickly in the absence of air to room temperature. It is believed that this procedure will be better understood from the following detailed example.

Example The raw materials utilized are reagent grade chemicals. To prepare one mole of the composition- 44.83 grams of nickel oxide containing very little impurity cobalt (less than 0.01% by weight), 72.89 grams manganous carbonate (assaying 60% MnO), and 171.7 grams iron oxide were weighed out and placed in a 1.2 litre rubber-lined ball-mill jar. The jar also had 2.78 kilograms of inch diameter steel balls therein. Enough water was added to make a slurry of the mixture, and the mixture was milled for a period of 16 hours. The slurry was removed from the mill, separated from the balls, and dried to a cake in a drying oven. The cake was forced through a 20-mesh sieve and then placed in a pure alumina crucible which was heated to a temperature of approximately 1750 F. and soaked at this temperature for one hour. When cool, this reacted powder was again ground in the ball-mill for 16 hours and dried as previously described. The dry cake was again broken u on a 20-mesh sieve. The binder, 2 /z% by weight polyvinyl alcohol in a aqueous solution, was then added and the mixture was dried. The dry mixture was then hand-sieved and the powder passing through a 100- mesh sieve and retained on a ZSO-mesh sieve was saved. Lubricants including 1% by weight of stearic acid were added and this powder was then carefully shaken through an 80-mesh screen. The powder was then pressed into the desired size toroids or cores.

The cores were carefully heated, the temperatures being slowly increased to 1000 F. to drive off the volatile binder and they were then fired to a high temperature of 2400 F. A controlled atmosphere surrounding the cores was maintained during the entire firing cycle. A suitable atmosphere is one that allows the material of the core to assume a composition essentially that represented by the formula M 0 in which M is a general symbol representing the metal atom present. A suitable atmosphere for the compositions described is carbon dioxide. Other gases such as prepurified nitrogen may be used. It is to be noted that air is an unsatisfactory atmosphere because it causes oxidation of the material to an oxygen content considerably greater than that given by the formula M 0 Hydrogen or pure carbon monoxide would also be unsuitable because the oxygen content would be reduced during firing to a content considerably less than that given by the formula M 0 The cores were fired at high temperature lying between 2350 and 2500 F. The at peak temperature ranged from 1 /2 to 3 hours. The cores were then cooled in the furnace by disconnecting the power. When the hot zone in the furnace reached a temperature between 1800 and 2000 F., the cores were moved from the hot zone to a region near room temperature and were cooled to room temperature in this location. They were not removed from the furnace in which they were surrounded by the controlled atmosphere, until they cooled to room temperature.

It should be understood that the above example is a typical procedure utilized for the preparation of the compositions of this invention. The processing may be changed when desired to compensate for deviations in the raw materials or to control the properties of the final product. As a result, a variety of cores can be obtained. As previously described, the two most important criteria for the successful production of the compositions of this invention are very thorough mixing of the material before firing and a controlled atmosphere during firing. After firing no further treatment of the cores is required.

The improved properties resulting from the novel compositions described are clearly shown when they are subjected to a standard pulse test program normally utilized to evaluate memory cores for the coincident current switching and storage application.

In Table II below, 1 is the amplitude of the full write or read current which is identified as I I =I which represents the disturbing current. The rise-time of the current pulse is t,, while the duration of the pulse is represented as i The voltage output of the core, read as it is switched from one stable state to another is shown as V The read-current pulse follows twenty disturbing pulses of amplitude I The distrubed zero voltage dV is read following twenty pulses of amplitude I equal to I but of opposite sign. The pulse repetition frequency was 40 kilocycles. The tests were conducted at C. The temperature limit recited indicates the temperature at which the properties of the core begin to decrease rapidly and severely.

TABLE H A. TEST SA)IPLE0.3O IN. O.D., 0.020 IN. I.D., HEIGHT:0.007 IN.

Composition Izv= )n IPW=IPR ma. X Y Z (ma t;r (1V1 dV. t. Tempera- Q4500.) (mv.) (mv.) 01sec.) ture Limit B. TEST SAi\IPLL 0.050 IN. O.D., 0 030 IN. I.D., HEIGHT-10.017 IN.

Composition I(W=I)R rw=Irn ma. ma. X Y Z t, (1V1 (W, t. Temperasee) (mv.) (mv.) see) ture Limit As can be seen from above Table II, the compositions of this invention which fall within the area ABCD of the figure possess outstanding properties. In order to use memory cores in the coincident-current application it is necessary that a partial write current of amplitude 50% of the full write current does not cause an appreciable voltage aV compared to that dV produced when a core is switched. It is seen from the above table that for ratios of I /I greater than 0.58 and often greater than 0.6, the ratio of dV to dV is large enough to permit satisfactory operation of the cores. Further, it is shown that this desirable circumstance persists up to a temperature of 60 C. for 30 mil cores and to 80 C. for 50 mil cores. In the latter situation, for which the disturb ratios are very great, 0.6, the further advantage is present, in that the cores with some sacrifice in useful temperature range, can be driven by currents of higher amplitude and made to switch faster. The required driving currents are sufiiciently low initially so that this particular operation is both practical and feasible. It can thus be seen that the cores of this invention can be operated using currents of the same magnitude as the magnesium-manganese ferrite cores. Equal or faster switching times are obtainable and the cores can operate without temperature compensation up to temperatures as high as 80 C. To establish this comparison, reference is had to Table III below which shows the change of pulse response behavior with temperature of a typical nickel-manganese-ferrous ferrite core of this invention comprised of 0.60 NiFe O MnFe O and F6304.

TABLE III IW=IR I1 W=Ir n 12, 1: Te rrp 6V1 dVz 15 13,,

In view of the above results, it should be apparent that outstanding new ferrite compositions have been discovered. Particularly, these compositions have been shown to possess properties that enable their use as cores in various computers taking advantage of the fast switching speeds and low temperature coefiicients.

We claim:

1. A ferromagnetic composition conststing of the relative mole percentages of nickel ferrite, manganese ferrite and ferrous ferrite lying within the area defined in the accompanying ternary diagram of the drawing by the solid lines AB, BC, CD and DA.

2. A ferromagnetic composition comprising 60 mole percent nickel ferrite, 20 mole percent manganese ferrite and 20 mole percent ferrous ferrite.

3. A ferromagnetic composition comprising mole percent nickel ferrite, 25 mole percent manganese ferrite and 20 mole percent ferrous ferrite.

4. A ferromagnetic composition comprising 40 mole percent nickel ferrite, 45 mole percent manganese ferrite and 15 mole percent ferrous ferrite.

5. A ferromagnetic composition comprising 40 mole percent nickel ferrite, 50 mole percent manganese ferrite and 10 mole percent ferrous ferrite.

6. A ferromagnetic composition comprising mole percent nickel ferrite, 30 mole percent manganese ferrite, and 10 mole percent ferrous ferrite.

7. A ferromagnetic composition comprising mole percent nickel ferrite, 15 mole percent manganese ferrite, and 20 mole percent ferrous ferrite.

8. A ferromagnetic composition comprising 65 mole percent nickel ferrite, 25 mole percent manganese ferrite, and 10 mole percent ferrous ferrite.

9. A ferromagnetic composition comprising 60 mole percent nickel ferrite, 25 mole percent manganese ferrite, and 15 mole percent ferrous ferrite.

10. A ferromagnetic composition comprising 50 mole percent nickel ferrite, 40 mole percent manganese ferrite, and 10 mole percent ferrous ferrite.

References Cited by the Examiner UNITED STATES PATENTS 4/1962 Gorter et al 25262.5 9/1962 Baltzer 252-625 

1. A FERROMAGNETIC COMPOSITION CONSISTING OF THE RELATIVE MOLE PERCENTAGES OF NICKEL FERRITE, MANGANESE FERRITE AND FERROUS FERRITE LYING WITH IN THE AREA DEFINED IN THE ACCOMPANYING TERNARY DIAGRAM OF THE DRAWING BY THE SOLID LINES AB, BC, CD AND DA. 